| A | B |
|---|
| lava | hot, melted rock that comes out of the earth |
| volcano | an opening in the earth out of which hot gasses, ash, and lava may pour |
| slope | the side of a mountain |
| Continental Divide | an imaginary line along the highest points of the Rocky Mountains that determines which direction rivers will flow |
| timberline | because of the elevation, trees do not grow above here |
| barrier | something that blocks the way or makes it difficult to get past |
| transcontinental railroad | a railroad that links the east and west coasts |
| labor | work |
| satellite | an object that orbits the earth |
| mileage table | a chart that shows distance between listed cities |
| boomtown | fast growing towns that grew up around discoveries of gold |
| trade-off | giving up one thing to get another |
| opportunity cost | the value of what one gives up to get something one wants |
| public land | land owned by the government |
| geyser | a spring that shoots hot water and steam into the air |
| conclusion | a decision or idea reached by careful thought and study |
| prediction | using what you know from past experience and information, to tell what you think will happen |
| terrace | a flat shelf of land dug into a mountainside |
| bartering | trading one kind of good for another without using money |
